Character Mesh Distorts Upon Keyframing
Edit: true answer for your problem is point 2

1)

If you want to move your character along the X axis for example, you need to move the armature (in Object mode), not the object itself: The object is parented to the armature, so it will follow the armature. So delete the keyframes you've created for the object and create keyframes for the armature.

To see the keyframes of the selected object only, enable this button on the bottom of the Dopesheet window, otherwise you'll see all the keyframes of all the objects of your scene.

Now select the character object (not the armature) and delete the keyframes you've probably created.



2)

Now, my first answer didn't fix your problem but I've found the anomaly. I can't explain how it happened but this will fix the problem: Go into the Outliner, you'll see that the Animation is part of the object while it should not be the case, so ctrl right click over Animation and Clear Animation Data